The invention relates generally to cooling systems and more specifically to a water-cooled magnetorheological fluid controlled combination fan drive and water pump.
Cooling systems are used on vehicles today to provide cooling to an engine during operation. Fan drives are typically driven by the engine crankshaft at a fixed ratio to cool engine coolant as it flows through a radiator. Thus, as the engine speed is reduced, as is the trend in vehicles today to reduce emissions, the fan drive speed is correspondingly reduced. Similarly, as the engine speed increases, the fan drive speed correspondingly increases. This increased fan drive speed causes the engine block temperature to cool to less than optimal levels, resulting in less than optimal conditions that can affect emissions and fuel economy.
One method to address these issues is to add a viscous fluid coupling to drive the radiator cooling fans. In a typical viscous fluid coupling, an input shaft drives an input coupling member (clutch) which is received within an output coupling member, and torque is transmitted from the input to the output, in the presence of viscous fluid, by means of viscous shear drag. The coupling normally includes some sort of valving which controls the amount of viscous fluid within a viscous shear chamber, thereby controlling the ratio of the output torque and speed to the input torque and speed. Typically, this valving comprises a valve member that is moveable to cover or uncover a fill port disposed between a reservoir and viscous shear chamber (operating chamber).
As is well known to those skilled in the art, the transmission of torque from an input coupling member to an output coupling member by means of viscous shear drag results in the generation of a substantial amount of heat. At least a major portion of the heat must be dissipated, or else the temperature of the viscous fluid will continue to increase, as the fan drive operates, until the fluid eventually begins to chemically break down and lose viscosity, resulting in less torque available to drive the fan drive.
To remedy this, viscous couplings have been developed with increased heat dissipation capabilities. For example, U.S. Pat. No. 6,021,747 discloses a viscous coupling that can be water-cooled, or cooled by the flow of engine coolant (the terms xe2x80x9cwaterxe2x80x9d and xe2x80x9ccoolantxe2x80x9d are used interchangeably). This minimizes the buildup of heat within the coupling, thereby preventing the chemical breakdown of the viscous fluid within the coupling.
One problem with currently available viscous couplings for fan drives is the complexity of the designs. Viscous fluid must be moved from a fluid reservoir chamber to a working chamber in order to couple or uncouple the input coupling member from the output coupling member. This requires a combination of the use of moveable valve members, valve wiper arms, and relief chambers to move the viscous fluid both into and out of the working chamber. This adds complexity and cost to the viscous coupling.
More importantly, currently available viscous couplings are either incapable of being controlled to provide instantaneous cooling to an engine block or require a period of time to increase or decrease the amount of cooling available to the engine block. This time lag may adversely affect fuel economy and emissions at various engine speeds and engine temperatures.
In addition to fan drives, cooling systems generally have a water pump for pumping cooled engine coolant from a radiator to an engine block in a closed system. These water pumps are either electric water pumps or water pumps controlled by drive mechanisms similar to those found on fan drives as described above. Similarly, these driven water pumps experience the same sort of problems of instantaneous control as the fan drives. Further, these water pumps add another degree of complexity to the cooling system that significantly increase the cost and space necessary to house the various associated components.
It is thus highly desirable to limit the complexity of the cooling systems by combining the fan drive mechanism and water pump into one element. It is also desirable to electronically control the fan speed and pumping capacity of the combined element to provide instantaneously control of the cooling capacity of the cooling system.
The above and other objects of the invention are met by the present invention that is an improvement over known cooling systems.
The present invention discloses a water-cooled magnetorheological fluid controlled combination fan drive and water pump. Magnetorheological fluid, normally thin, thickens between a pair of cylindrical drums when a magnetic field is applied. This thickening allows the magnetorheological fluid to shear between the drums and transmits torque from a driven ring to a drive ring. The driven ring is coupled to an impeller assembly that rotates to provide engine coolant flow to the engine. Further, the drive ring is coupled to an output shaft that is coupled to a fan tat rotates to provide cooling air flow to a closely coupled radiator. A stationary coil mounted within the water-cooled magnetorheological fluid controlled combination fan drive and water pump is electrically excited to create the desired magnetic field. The amount of electrical excitation is controlled as a function of engine speed and engine block temperature to maximum fuel economy and minimize emissions at various engine temperatures and speeds.
Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.